Patent Application
20240019206
The invention relates to a cryogenic process for recovering valuable components, in particular hydrogen, from a hydrogen-rich feed gas, preferably a hydrogen-rich natural gas, wherein hydrocarbons with two or more carbon atoms, methane and nitrogen are separated in at least 3 separation columns.
In recent times, hydrogen has increasingly been seen as a clean source of energy for mankind, as its combustion produces only water. Industrially produced hydrogen is used in abundance in chemical processes and its role as an energy carrier is driving the energy industry to massive investment, increasingly including the use of hydrogen for energy storage.
Hydrogen is usually obtained from residual gas streams from chemical processes, such as reforming or cracking processes. Membrane and/or pressure swing adsorbers are used to enrich and/or isolate the hydrogen from these residual gas streams. These residual gas streams usually comprise methane, hydrocarbon mixtures of different chain lengths, preferably light hydrocarbons, carbon monoxide and carbon dioxide.
The recent discovery of various natural hydrogen sources underscores the economic interests in exploiting naturally occurring hydrogen in continental mainland areas in the future. For this, processes are needed that can make the extraction of hydrogen from these natural hydrogen sources cheaper than the industrial production from fossil fuels or by electrolysis. Due to the size of the already discovered hydrogen-containing natural gas sources with high potential production volumes, for example the hydrogen-rich natural gas source in Bourakebougou (Mali), the pressure swing adsorption and membrane technologies known in the state of the art are technically not able to process satisfactory production volumes in a cost-efficient manner. This requires large-scale plants with capacities of, for example, 1000 t/day or a thermal output of approx. 1.5 GW, which corresponds to a flow rate of approx. 500,000 normal cubic meters/h (Nm3/h).
The aim of the present invention is therefore to provide a comprehensive process which has the capacity of large-scale plants, efficiently and cost-effectively separates large production quantities of a hydrogen-rich feed gas, in particular a hydrogen-rich natural gas, into the valuable components contained therein and, if necessary, makes these available for further processes after adjusting the purity. Since the natural hydrogen-rich natural gas sources found so far are located in geographical areas that are less industrialised (e.g. in Mali), an integrated process is advantageous here that separates all the valuable components present in the feed gas as efficiently, cost-effectively and comprehensively as possible on an industrial scale and makes them available for further uses or processes or as an energy source. Of course, such a process is also advantageous for large-scale industrially produced hydrogen-rich feed gases, especially against the background of the increasing use of hydrogen as an energy source in the automotive and other industrial sectors.
Details of the hydrogen-containing natural gas source in Mali described in the prior art are described by Prinzhofer et al. in the International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydgene.2018.08.193.
To solve this problem, a cryogenic process for recovering valuable components, in particular hydrogen, from a hydrogen-rich feed gas, preferably a hydrogen-rich natural gas, is described, wherein hydrocarbons with two or more carbon atoms are removed in a first separation column, methane is removed in a second separation column, and nitrogen is removed in a third separation column.
In a first aspect, the invention relates to a cryogenic process for recovering valuable components, in particular hydrogen, from a hydrogen-rich feed gas, preferably a hydrogen-rich natural gas, comprising the following steps:
For the purposes of the present invention, feed gas means a hydrogen-rich gas with a hydrogen content of 50% by volume or higher, which originates from an industrial process or from a natural gas source, which comprises the valuable components hydrogen, methane, hydrocarbons with two or more carbon atoms and nitrogen and which serves as the starting gas of the cryogenic process according to the invention.
The term feed fraction means the gas arriving at the respective separation column, which is passed through the corresponding separation column and thereby separated into at least 2 fractions, an overhead fraction and a bottom fraction.
Natural gas in the sense of the present invention means a gas formed by naturally occurring processes below the earth's surface or in the earth's interior. The hydrogen-rich natural gas preferably originates from a natural gas source.
The hydrogen-rich feed gas, preferably hydrogen-rich natural gas, has a hydrogen content of 50 to 99.9 vol %, preferably 70 to 99.9 vol % hydrogen, particularly preferably 90 to 99.9 vol % hydrogen.
Furthermore, nitrogen, methane and noble gases, in particular helium, neon and argon, and hydrocarbons with two or more carbon atoms, can be included in the feed gas, in particular natural gas, as additional components. In lower concentrations, in particular between 0 and 10 vol-%, carbon dioxide can also be included, whereas carbon monoxide and sulphur components may be present in concentrations between 0 and 0.5% by volume.
In a further embodiment, the hydrogen-rich feed gas, in particular the hydrogen-rich natural gas, has as main constituents a hydrogen content of between 50 and 99.9 vol %, a methane content of between 0.02 and 40 vol % and a nitrogen content of between 0.02 and 30 vol %, preferably a hydrogen content of at least 70 vol %, a methane content of at most 20 vol % and a nitrogen content of at most 20 vol %, particularly preferably a hydrogen content of at least 90 vol %, a methane content of at most 10 vol % and a nitrogen content of at most 10 vol %,
In the cryogenic process according to the invention, the first, second, third, fourth and fifth separation column is advantageously a rectification column.
In the cryogenic process according to the invention, the cold supply is preferably provided at least in part by one or more refrigeration cycles.
In the process according to the invention, the cooling and at least partial liquefaction of the hydrogen-rich feed gas, preferably the hydrogen-rich natural gas, takes place in separation columns, preferably rectification columns, against the refrigerant or refrigerant mixture in at least one heat exchanger (E1).
In a further aspect of the invention, the raw gas (B0), i.e. the hydrogen-rich feed gas, in particular the hydrogen-rich natural gas from the natural gas source, is pre-purified (R) by removing one or more constituents of the feed gas that would freeze out in the cryogenic part of the plant. Such constituents are particularly selected from the group consisting of water, carbon dioxide, hydrogen sulphide, mercaptans and mercury compounds, in particular mercury, or combinations thereof. These components can be removed by means of adsorption and/or absorption processes as part of the pre-cleaning process.
As a rule, natural gas wells, in particular hydrogen-rich natural gas wells, contain water which has to be removed in the course of pre-cleaning, pre-treatment or drying. In the case of natural gas sources that are already inherently very low in carbon dioxide, hydrogen sulphide, mercaptans and/or mercury compounds, in particular mercury, —at least in partial fractions of the production—or possibly do not contain any of these components at all, further pre-cleaning can be omitted where appropriate. Hydrogen-rich feed gases from industrial processes comprising the same constituents are treated accordingly. In one aspect of the present invention, a hydrogen-rich raw gas from a natural gas source is pre-purified and thereby at least the water component is removed, preferably carbon dioxide, hydrogen sulphide, mercaptans and/or mercury compounds, in particular mercury, are removed by pre-cleaning.
If hydrogen-rich feed gas from industrial processes is used as feed gas, which does not comprise any of the components described above, which are to be removed in the course of pre-cleaning, pre-treatment and/or drying may be omitted.
In the process according to the invention, the raw gas, in particular the hydrogen-rich natural gas, is preferably pre-compressed before pre-cleaning.
According to the invention, the valuable components contained in the raw gas, in particular hydrogen, hydrocarbons with two or more carbon atoms, methane, nitrogen are separated from the raw gas or pre-purified raw gas in the separation columns T1 to T3, preferably rectification columns. It is advantageous to compress the raw gas to a pressure between 20 and 50 bar before liquefying it. Particularly in the case of the comparatively valuable component hydrogen, recovery at high pressure is desirable, as the hydrogen is usually fed to a further application, e.g. compression.
The raw gas (B1) rich in hydrogen, in particular natural gas rich in hydrogen, which may have been pre-dried and/or pre-purified and may be present at a higher pressure, is fed to the first separation column (T1), preferably rectification column, after cooling and possibly partial condensation in heat exchanger E1, via a line in which an expansion valve may be provided optionally, and is separated in this column into a liquid and a gas fraction. Generally, in the corresponding separation columns, the liquid phase is called the bottom product and the gas phase is called the overhead product.
According to the process of the invention, the bottom product from the first separation column T1, preferably rectification column, in particular C2, C3 hydrocarbons and higher hydrocarbons, is fractionated in a further fractionation, i.e. a fourth separation column T4, preferably rectification column, to ethane gas (B3) and LPG (B2). The bottom product of the separation column T1 can initially serve as a refrigerant in E1 and, possibly after throttling, be fed in two phases into the separation column T4.
Optionally, in a further aspect of the invention, a partial stream of the hydrogen-rich feed gas, after optional pre-cleaning R (B1), can be fed directly into the lower part of separation column T1, bypassing heat exchanger E1. As a result, the reboiler of the separation column T1 is at least partially relieved.
At the top of the separation column T1, preferably rectification column, the fraction containing at least methane, nitrogen and hydrogen (overhead product) is withdrawn. This fraction is further cooled in heat exchanger E1 and then fed to the second separation column T2, preferably rectification column, via a line in which an expansion valve can be provided optionally.
Optionally, in a further aspect of the invention, a partial stream of the overhead stream of the separation column T1 can be fed directly into the lower part of separation column T2, bypassing heat exchanger E1. This has the effect that the reboiler of the separation column T2 is at least partially relieved (not shown in
According to the invention, the overhead condenser is cooled via heat exchanger E1 of the first separation column T1, preferably rectification column, by a refrigerant or refrigerant mixture or a partial flow of the refrigerant or refrigerant mixture.
The overhead condensers of all separation columns, preferably rectification columns, may be either plate fin heat exchangers, preferably multi-flow plate fin heat exchangers, spiral wound heat exchangers, preferably multi-flow spiral wound heat exchangers, TEMA heat exchangers, series of spiral wound heat exchangers and/or plate fin heat exchangers connected in series and arranged in or above the respective separation column T, preferably rectification column T, whereby an arrangement above the rectification column allows to avoid a reflux pump.
By varying the column height and the cold supply, the impurities in the respective overhead products can be kept within narrow limits. For example, the ethane content of the fraction withdrawn overhead in separation column T1 can be set almost arbitrarily, namely between approx. 10 ppmV to a few vol-%, preferably less than 2% vol, particularly preferably less than 1% vol. The methane content in the bottom product of the separation column T1 can be adjusted almost arbitrarily, namely between approx. 1 ppm to some vol-%, preferably less than 2% vol, particularly preferably less than 1% vol.
The valuable components separated at the top of the first separation column T1, preferably rectification column, comprising at least one or more valuable components from the group consisting of methane, nitrogen and hydrogen, are, after further cooling in heat exchanger E1, fed to separation column T2, preferably rectification column, via a line in which an expansion valve can be provided optionally, and are separated in T2 into a liquid and a gas fraction.
Optionally, in a further aspect of the invention, a partial stream of the overhead stream of separation column T2 can be fed directly into the lower part of separation column T3, bypassing heat exchanger E1. This has the effect that the reboiler of separation column T3 is at least partially relieved (not shown in
According to the invention, the overhead condenser E1 of the second separation column T2, preferably rectification column, is cooled by a refrigerant or refrigerant mixture or a partial flow of the refrigerant or refrigerant mixture.
The methane-rich bottom product from second separation column T2, preferably rectification column, is either heated in heat exchanger (E1) and compressed and recovered as methane gas (B4) or further cooled by means of heat exchanger (E1), expanded and recovered as LNG.
The valuable components separated at the top of separation column T2, preferably rectification column, comprising at least one or more valuable components from the group consisting of nitrogen, helium and hydrogen are, after further cooling, fed via a line in which a pressure relief valve can be provided optionally, to the third separation column T3, preferably rectification column, and separated in this into a liquid and a gas fraction.
Part of the nitrogen-rich bottom product of separation column T3 can be expanded, heated in heat exchanger (E1) and fed into the refrigeration cycle of E1 as refrigerant or a component of the refrigerant. The nitrogen-rich bottom product can also be heated without expansion in E1 and further used as high-pressure nitrogen (B5).
Alternatively, the bottom product of separation column T3 (high-pressure LIN) can be expanded and serve as first refrigerant stage for the liquefaction of hydrogen or helium.
If carbon monoxide is present in the raw gas, this is enriched in the nitrogen-rich bottom product of the third separation column T3, preferably rectification column, and can preferably be converted to carbon dioxide at the warm end of the process with the aid of added oxygen in an additional process unit. Nitrogen with small amounts of carbon dioxide is recovered as a valuable product, which can be used and/or fed to further processes.
In the process according to the invention, the helium possibly contained in the hydrogen-rich overhead product of the third separation column T3, preferably rectification column, is separated into the two components helium and hydrogen after further cooling in a fifth separation column, in particular a hydrogen separation column (T5), preferably rectification column, split into the two components helium and hydrogen by rectification or at least one-stage depressurisation, freed of residual impurities separately in cryogenic standard liquefaction plants, if necessary, liquefied and stored, preferably in vacuum-insulated special tanks.
According to the process of the invention, the hydrogen-rich overhead product of the third separation column T3, preferably rectification column, is heated (B6) in heat exchanger (E1), compressed and fed into a pipeline. Alternatively, it can be freed from residual impurities in a standard hydrogen liquefaction plant, liquefied and stored, preferably in vacuum-insulated special tanks.
In the further course of the process according to the invention, the hydrogen overhead product from separation column T3, preferably rectification column, can first be purified by means of adsorption in a special unit according to the state of the art, then liquefied and stored, preferably in vacuum-insulated special tanks.
Depending on the number of stages of the respective separation columns, in particular rectification columns, and the cold/heat supply, the purity of the respective products is adjusted. In the process according to the invention, the methane-rich bottom product of separation column T2, the hydrogen-rich overhead product and the nitrogen-rich bottom product of separation column T3 and the ethane-rich overhead product of separation column T4 are recovered according to the cold supply in E1 as LPG product (B2) or ethane product (B3) or methane product (B4) or nitrogen product (B5) or hydrogen product (B6) as valuable products in their purity and then made available for other processes or utilisations/purposes. The products of separation column T5, i.e. the hydrogen bottom product or helium overhead product, are also adjusted in their purity in separation column T5. The helium overhead product is first purified by means of adsorption, then liquefied and stored, preferably in vacuum-insulated special tanks. The bottom product hydrogen is purified by means of adsorption and stored, preferably in vacuum-insulated special tanks.
In a preferred aspect of the invention, the condensers of the separation columns, preferably rectification columns, T1 to T4 and the reboilers of T1 to T3 are connected to E1 or integrated in E1.
The at least one heat exchanger unit E1 used in the process according to the invention is designed as a multi-flow plate fin heat exchanger or spiral wound heat exchanger, in particular as a series of spiral wound heat exchangers and/or plate fin heat exchangers connected in series, preferably in multiple subdivision according to the temperature profile of the separation process, in order to ensure exergetically favourable temperature differences over the entire cooling and in preferably multiple parallel connection—depending on the capacity of the installation.
The cold supply of the separation process of the separation columns, preferably rectification columns, (T1 to T4) according to the process of the invention is provided either
The cryogenic process according to the invention for the recovery of hydrogen, hydrocarbons with two or more hydrocarbons, methane and nitrogen from hydrogen-rich feed gas, in particular hydrogen-rich natural gas, as well as further advantageous embodiments thereof, are explained in more detail below on the basis of the embodiment example shown in the figure.
Examples of the composition for hydrogen-rich natural gas sources for which the cryogenic process according to the invention is applied are shown in Table 1 and 2 as
Process:
Cooling Circuit:
Miscellaneous:
In the following, in
This cryogenic process is executed by means of rectification columns. The feed fraction containing at least methane, nitrogen and hydrogen is fed via line 1 to a pre-cleaning unit R if required. At low feed pressures, the feed fraction is pre-compressed to a pressure between 20 and 50 bar, if required. Furthermore, if water, carbon dioxide and mercury compounds, especially mercury, are present, carbon dioxide and mercury removal as well as drying are usually carried out. If sulphur components are present, these are also removed by means of pre-cleaning.
The feed fraction, which may have been pre-treated in this way, is then fed via line 2 to heat exchanger E1, where it is cooled and partially condensed. Heat exchanger E1 is usually designed as a plate fin heat exchanger or as a spiral wound heat exchanger. In case of appropriate large capacities, several heat exchangers arranged in parallel and/or in sequence are provided if necessary. Cooling and liquefaction of the feed fraction takes place against at least one refrigeration cycle of any design, which is shown in the figure only schematically by the pipe sections 21 to 27, which will be discussed in more detail below. This refrigeration cycle is preferably designed as an expander or mixed refrigerant cycle.
The cooled and possibly partially condensed feed fraction is fed to rectification column T1 (ethane separation column) via line 3, in which an expansion valve a can be situated, and separated into a liquid and a gas fraction in this column.
If the hydrogen-rich feed gas, in particular the hydrogen-rich natural gas (B1) contains heavy hydrocarbons, these can be fed with the ethane-rich bottom product from the rectification column T1 via line 6 to heat exchanger E1, heated and then fed via line 16, in which a pressure relief valve e can be provided, to rectification column T4 (propane separation column) and separated into an ethane product as the top product of the rectification column T4 (B3) and into an LPG (B2) as the bottom product of the rectification column T4. Alternatively, line 6 can join directly line 16, bypassing heat exchanger E1.
Part of the feed fraction can also be fed directly into the rectification column T1 as stripping gas, bypassing heat exchanger E1, in order to at least partially relieve the reboiler.
At the top of rectification column T1, methane and nitrogen as well as the lighter components, in particular the hydrogen-containing fraction, are withdrawn via line 4. This fraction is further cooled against the refrigerant in heat exchanger E1 and then fed to rectification column T2 (methane separation column) via line 5, in which an expansion valve b can be situated, and separated into a liquid and a gas fraction in this.
A methane-rich liquid fraction with a nitrogen content of typically less than 3% by volume is withdrawn from the bottom of rectification column T2 via line 7, heated in heat exchanger E1 and fed to its further use as methane product (B4). Alternatively, the methane-rich liquid fraction can be subcooled against the refrigerant or refrigerant mixture of the refrigeration cycle in E1 and fed via line 8 to a storage tank S as LNG product after expansion in valve f.
Tank return gas from storage tank S can be compressed in one or more stages if necessary and discharged at the plant boundary. Alternatively, the tank return gas can also be fed into a fuel gas system.
At the top of rectification column T2, nitrogen and lighter components, in particular the hydrogen-containing fraction, are withdrawn via line 9. This fraction is further cooled against the refrigerant in heat exchanger E1 and then fed to rectification column T3 (nitrogen separation column) via line 10, in which an expansion valve c can be situated, and separated into a liquid and a gas fraction in this column.
The nitrogen-rich bottom product of T3 can either be heated in E1 via line 12, which then passes into line 14, and reused as a nitrogen product (B5) or at least a partial flow from line 12 can be expanded to the pressure of the refrigeration cycle in throttle valve h and used there as refrigerant or at least as part of the refrigerant.
The nitrogen-rich bottom product of T3 can also be fed to the hydrogen liquefaction plant and the helium liquefaction plant via line 12, expanded and used there as a refrigerant.
The hydrogen-rich overhead product of T3 is fed via line 11 to heat exchanger E1, where it is warmed up and is available for further use as hydrogen product (B6). The hydrogen product can either be compressed and fed into a pipeline or, possibly after compression, fed into a standard hydrogen liquefaction plant.
If the hydrogen-rich overhead product of T3 contains noble gases such as helium, the overhead product of T3 can, after further cooling, be fed via line 13, possibly via an expansion valve d, to a further separation column T5 (hydrogen separation column), alternatively to one or more separators, in order to separate helium and any other noble gases present from hydrogen. Subsequently, the overhead product of T5 can be fed to a noble gas liquefaction plant (B8), preferably a helium liquefaction plant, and the bottom product of T5 can be further processed to liquid hydrogen (B7). The liquid products are then stored in vacuum-insulated special tanks.
According to the invention, the process is supplied with cold by a refrigerant or refrigerant mixture and by heating the products in E1. The figure shows an example of a nitrogen expander cycle; alternatively, a nitrogen-methane expander cycle or a mixed refrigerant cycle may also be optimal. Several identical or different refrigeration cycles can also be applied.
At the warm end of E1, the low-pressure refrigerant flow is fed into a single- or multi-stage cycle compression via line 21, the final pressure of the expander cycle is set via the compressors coupled to the expander(s). The high-pressure cycle flow cooled against air or water is then precooled via line 22 in E1. At a certain temperature set by the process optimisation, a partial flow (line 23) is withdrawn and expanded in expander X1 to provide cooling in E1 (24). The high-pressure main stream is further cooled in E1 (25) and finally expanded in X2 (26), heated in E1, mixed with the stream to X1, further heated in E1 and fed to the circuit compression 21. The refrigerant component nitrogen can preferably be added in the cold part of the cycle 27, but also after heating the HP nitrogen (B5).
Instead of a pure nitrogen expander cycle, a nitrogen-methane expander cycle can be used, whereby the methane portion of the refrigerant is preferably obtained from the methane product (B4) or the bottom product of T2. In this cycle, the second expander compressor X2-C2 can possibly be omitted and replaced by a throttle valve g.
The heat exchangers that provide the overhead refrigeration for the various rectification columns (T1, T2, T3, T4) can be designed either as plate fin heat exchangers, coiled wound heat exchangers or TEMA heat exchangers and arranged in or above the respective rectification columns, whereby an arrangement above the rectification columns makes a reflux pump obsolete. By varying the column height and the cold supply, the impurities of the respective overhead products can be kept within narrow limits, e.g. the methane content in the fraction withdrawn via line 9 can be set almost arbitrarily, namely between approx. 1 ppm to a few [vol-%, preferably less than 2% vol, particularly preferably less than 1% vol.
The process according to the invention for recovering valuable components from a hydrogen-rich feed gas, in particular a hydrogen-rich natural gas, can be used advantageously at hydrogen contents of 50 vol-% and above. As long as the hydrogen product and the methane product are not liquefied, even comparatively high nitrogen and methane contents in the feed fraction have only a subordinate effect on the total energy requirement of the process according to the invention, since part of the cold is recovered by heating the products hydrogen, nitrogen and methane in E1.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2020 130 946.5 | Nov 2020 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/082545 | 11/22/2021 | WO |
